In this work, we design and successfully fabricate novel Bi2O3 quantum dot (QD)-decorated BiVO4 nanofibers by a direct heat treatment of as-spun fibers. The Bi2O3 QDs with a size of 5-15 nm are well dispersed on the surface of the BiVO4 nanofibers with a diameter of 400-700 nm to form a Bi2O3 QD-decorated BiVO4 nanofiber photocatalyst. Based on the phase separation mechanism and the properties of solvents, a possible formation process of the Bi2O3 QD-decorated BiVO4 nanofibers has been proposed. The BiVO4 nanofibers decorated with Bi2O3 QDs exhibit much better photocatalytic performance than pure BiVO4 nanofibers. Photocurrent responses and electrochemical impedance spectra prove that decorating BiVO4 nanofibers with very small Bi2O3 QDs can effectively promote the separation of photoinduced carriers, which is beneficial for photocatalytic properties. More significantly, this work is relevant to environmental purification and photoelectrochemistry.